Added support for checking if lockScreen and notificationCenter settings are enabled

[alexhernandez]

Summary

I was working on a project and needed access to know if notifications were enabled for lockScreen and notificationCenter when firing checkPermissions().

Test Plan

What's required for testing (prerequisites)?

What are the steps to reproduce (after prerequisites)?

To test fire checkPermissions() and you should get an updated object that includes lockScreen and notificationCenter.

Alternatively, you can also run the /example and press "show enabled permissions".

Before this commit:

{
    "alert": true,
    "badge": true,
    "sound": true,
}

After commit:

{
    "alert": true,
    "badge": true,
    "sound": true,
    "lockScreen": true, 
    "notificationCenter": true,
}

Compatibility

OS	Implemented
iOS	✅
Android	❌

Checklist

• I have tested this on a device and a simulator
• I added the documentation in README.md
• I mentioned this change in CHANGELOG.md
• I updated the typed files (TS and Flow)
• I added a sample use of the API in the example project (example/App.js)

[Naturalclar]

@alexhernandez Thanks so much!